In an infrastructure network, an access point (AP) may be configured with a Basic Service Set (BSS). Further APs may also have respective BSSs with the combination thereof with the first access point creating an Extended Service Set (ESS). Initially, a client such as a mobile unit may be connected to one of the APs based on, for example, location. As the client moves, it is possible to move out of the BSS of the currently connected AP. That is, the client is moving out of the coverage area of the currently connected AP and moving into a coverage area of a different AP in the same ESS (i.e., roam). In such a case, the client starts a scanning process to find the APs in the environment and determine a more appropriate AP in which to connect.
Conventional methods of roam scanning include an active scan or a passive scan to find the appropriate AP in which to connect and determine a power at which the packets from each AP are received by the client. An active scan allows the client to actively change to a channel being scanned to broadcast a probe request and subsequently wait for a response. A passive scan allows the client to change to a channel being scanned and wait for a periodic beacon from an AP utilizing the channel. With an active scan, if the client wants to finish the scanning process quickly and the channel does not have any regulatory constraint, the client may start sending probe requests with a Service Set Identifier (SSID) in each channel and stay in the respective channel for a predetermined time to receive the probe responses from the APs. Through these probe responses from the APs, the client may choose a better AP and connect to it for a roam.
Despite active scanning being quicker than passive scanning, active scanning also takes a considerable amount of time. For example, if 13 channels are allowed in a particular country in the 802.11 b/g band and the client waits a predetermined amount of time in each channel during the active scan such as 20 ms, the client will spend 13×20 ms which is 260 ms spent for scanning alone. If all the supported bands are included for scanning, this time delay for scanning will still be higher. Conventional methods may restrict the client from scanning every channel and make the client only scan channels in which the APs of the ESS are configured. Such methods will still spend a predetermined amount of time based upon the number of channels to be scanned. In addition, a legacy method of active scanning includes a problem in that the number of probe responses received in a channel will be equal to the number of APs that hear the probe request sent by the client. Thus, if, for example, three APs in the same ESS are configured in a single channel and all hear the probe request, the number of probe responses received in that channel will also be three. Despite appearing insignificant, such a scanning may have a considerable effect on a channel with high data traffic. A further consideration for conventional methods includes the client choosing not to transmit or receive any data during the entire scan process. Still another consideration is the scanning process may entail scanning a single channel, returning to the home channel, transmit/receive data packets and go to a different channel for scanning. Regardless of the scanning being performed, the AP has to buffer the frames for the client during the scan and transmit them to the client once it comes back to the home channel. If any time critical data transmissions are in progress, even a 20 ms delay may be unaffordable for the client and the AP.
Accordingly, there is a need for a method and system for providing an active roam scanning that requires less time.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.